Safety devices for compressed gas containers



April 24, 1956 R. WACHTELL SAFETY DEVICES FOR COMPRESSED GAS CONTAINERSFiled May 28, 1952 CYLINDER n my I 5.

IN V EN TOR. 160/042 ll/mzwrsu.

ATrQeA sys United States Patent SAFETY DEVICES FOR COMPRESSED GASCONTAINERS Richard Wachtell, Mamaroneck, N. Y., assignor to AmericanElectro Metal Corporation, Yonkers, N. Y., a corporation of MarylandApplication May 28, 1952, Serial No. 290,389

7 Claims. (Cl. 220-89) This invention relates to safety devices forcompressed gas containers, and more particularly to safety devices knownas frangible disc safety devices.

Generally, two types of safety devices are used on compressedgascontainers depending upon the amount of gas pressure within thecontainer. High pressure gas containers, such as those containingoxygen, use a safety device consisting of a thin copper disc inserted ina specially designed nut attached to a fitting on the valve stem on theupper portion of the gas cylinder. The physical dimensions of the copperdisc are chosen so that it will fracture or burst at a specifiedpressure thereby permitting the confined gas to escape and avoiding thedangerous possibility of the increased gas pressure fracturing the wallsof the container and propelling it through the air. Because the coppermaterial is subject to conditions of creep under the continually appliedload of the compressed gas, it is backed up by a low temperature fusiblealloy'; the theory being that only heat might cause an increase in thepressure of the gas Within the cylinder, and that under conditions ofheat, the fusible alloy would melt permitting the copper disc to expandback into the rupture chamber and fracture.

Low pressure gas cylinders such as those containing acetylene gas,merely have fusible metal plugs which melt under conditions of heat, itbeing impossible to manufacture and handle the thin bursting discsnecessary for fracturing under such low pressures.

One of the main disadvantages of these safety devices is that localheating at the base or at the sides of the gas container would not meltthe fusiblealloy although the gas pressure in the cylinder rises highenough to burst it. Another disadvantage is that the fusible alloy isitself subject to creep under the continually applied load of thecompressed gas. i

The present invention overcomes these difiiculties by providing afrangible disc safety device having a creepresistant bursting disc whicheliminates the needfor a fusible alloy backing and in addition providesfor the slow rather than the explosive escape of gas through thebursting disc, since the danger of fire due to the escaping gases ismaterially reduced under these circumstances.

In accordance with the invention, a bursting disc consisting of asubstantially strong creep-resistant porous matrix or skeleton of alloysteel, tungsten carbide, bronze, beta brass or any other suitable strongmaterial is produced and thereafter its pores are completely filled witha low-temperature fusible material. With such a construction, theskeleton provides the strength and resistance to creep desired in thebursting disc, while the fusible alloy filling its pores provides thegas seal. With a disc of such design, failure will occur either throughover-pressure (by bursting of the disc in the normal manner), or in theevent of local heating bymelting out of the fusible alloy withconsequent loss of the gas through the now porous bursting disc.

One object of the invention is to provide a safety device for compressedgas containers having a creep-resistant bursting disc, and a method formaking such a bursting disc.

Another object of the invention is to provide a safety device forcompressed gas containers which will permit the slow escape rather thanthe explosive escape of gas upon failure of the safety device.

A further object of the invention is a method for manufacturing suchsafety devices on a production basis using unskilled labor.

The foregoing and other objects of the invention will be best understoodfrom the following detailed description of exemplifications thereof,reference being had to the accompanying drawings, wherein:

Fig. 1 is an elevational view of the upper part of a compressed gascontainer containing the safety device of the invention; g

Fig. 2 is a cross-sectional view of a frangible disc safety devicecontaining one form of a bursting disc of the invention; and

' Fig. 3 is a photomicrograph (X200) of the structure of the burstingdisc shown in Fig. 2.

Referring to Fig. 2, in the specific form shown, the safety device 10 isattached to the valve stem of the gas cylinder 11 by a hollow laterallyextending pipe extension 12, just prior to the outlet control valve 13.The safety device 10 contains a bursting disc 15 held in its operativeposition generally perpendicular to the longitudinal axis of the pipeextension 12 by a back-up nut 16.

' 'The back-up nut 16 comprises an inside threaded cupouter end ofthehollow pipe extension 12 and an inner facing shoulder 17 of the back-upnut 16 to provide a barrier through which the compressed gas in thehollow pipe extension 12 cannot flow. A circular washer 18, of fiber forinstance, having a center opening is interposed between the facingsurfaces of the pipe extension 12 and the bursting disc 15 to preventany gas leakage through the threaded contact surface portions of theback-up nut 16 and thepipe extension 12.

When the pressure of the gas Within the pipe extension 12 exceeds aspecified amount, the bursting disc 15 will expand back into a rupturechamber 19 and fracture. The gas will flow past the fractured burstingdisc 15, through the rupture chamber 19 and out through a blow out hole29, inthe rear of the back-up nut 16. p

In the form shown the bursting disc 15 comprises asubstantially'strong-rigid-porous skeleton having its pores filled witha low temperature fusible'alloy. The skeleton material can be anysuitable strong material that will not creep under the normal workingpressures of the compressed gas, such as alloy steel, tungsten-carbide,bronze and other like strong materials. The fusible alloy may be anymetal or alloy that will melt at low temperatures of the order of aboutISO-250 F. Woods metal, an alloy of bismuth, lead, tin and cadmium, isvery satisfactory as the fusible alloy.

There will now be described one practical way of making a bursting discin accordance with the principles of the invention using bronze as theskeleton material and Woods metal as the easily fusible alloy.

A desirable method for producing the bursting disc 15 in accordance withthe invention is by using powdered metallurgical techniques.

In general, the bronze metal may be pulverized or disintegrated to formsuitable sized powder particles. The powder particles are then compactedand heated at an elevated temperature in a mold having the desired shapeof the bursting disc 15 so as to form a substantially strong rigidporous structure. Thereafter, the soproduced porous structure isinfiltrated with the low temperature fusible alloy.

*Fig. 3 shows a-photomicrograph (X200) of the structure .obtainedin .acemented bronze powder particle porous structure infiltrated with Woodsmetal. The cross-hatched large oval particles 25 are the bronzeparticles; ithe .ribbon like structure 26 abutting the bronze particlesis a tin-rich layer which normally exists onthe surface of the bronze asmanufactured; the-dotted:intergranular phase 27 is the eutectic of'thefusible alloy.

1n ordertozenable those skilled in the art-to readily practice theinvention .but without limiting the scope thereof, I will now .giveamoredetailed description of a practical method for forming thebursting'disc in accordance with the invention.

The bronze metal .is disintegrated or pulverizedby ballmilling or otherlike disintegrating :processes into fine powder particles of suitablesize. Thereafter the bronze powder particles :are formed into -'the*desired shape f the "bursting disc by compacting -in a -mold having acavity contour conforming to thedesired shape.

The compacted particles are then heated at an elevated temperature so asto give-the compactedbody the desired physical strength and rigidnessand to form a porous matrix. The bronze powder particles may be looselypacked in .a mold and thereafter sinter'ed while still in the mold in aprotective atmosphere (such as'partially combusted natural gas orproducer gas) at aitemperature of the order of 800 C. Bronzepowders'sinter easily and need not be prepressed'but other powders maybe green pressed, i. e., pressed before sintering.

In order to manufacture the safety device in accordancewith theinvention on aproduction'basispit is necessary that the porosity of thecemented bronze powder body be controlled within extremely close-limitsin order that each unit he identical in physical properties to thepreceding unit so that each safety device will fail or fracture at thesame proper bursting pressure.

To this end it has been found to be advantageousto employ sphericalpowders in forming the bursting disc, since thegeometry of the stackingof the spherical .powders will give good reproducible results.

The completed porous matrix or skeleton is then'ready for infiltration.The porous matrix .or skeleton must be completely infiltrated by the lowtemperature fusible alloy else the .gas will :gradually leak through thebursting disc. Because of the low. melting point of the fusible alloys,infiltration must be carried out at temperatures of the order betweenabout 200 F. and about300 F. This is a region in which hydrogen nolonger actsas a reducing agent or flux for any oxides that will haveformed in the :porous skeleton.

In order to reduce any oxides that may have formed within the porousskeleton so that complete infiltration will result, it has been founddesirable to employ liquid fluxes, such as hydrochloric acid plusalcohol or liquid soldering flux, or other like liquid fluxes.

The technique employed in infiltrating the bronze porous matrix orskeleton is to first impregnate the skeleton body with the liquid fluxas by immersing the body in the liquid flux. Thereafter, the impregnatedskeleton body is slowly immersed in -a pool of *the various other.modifications and applications of the same.

It is accordingly desired that in construing the breadth of the approvedclaims they shall not be limited to the specific exemplifications of theinvention described herein.

Iclaim:

1. In a safety relief device for gases under pressure, the combination'of a tank having a discharge duct :and a safetybursting disk providinga sealing closure for said duct, saicllbursting disk comprising .aporous skeleton body of cemented metal particles to provide a strongcreep resistant body, the pores of said skeleton body being filled witha readily fusible material which melts at temperatures above normal topermitgas'toescape through said pores.

'2. ln a safety relief device for gases under pressure, the combinationof a tank having a discharge 'duct and a safety'bursting disk providinga sealing closure for said duct, said bursting disk comprising a porousskeleton body of cemented metal particles to provide a strong -creepresistant body, the pores of said skeleton body being filled with areadily fusible materialwhich melts at about approximately to 250 F. to'perrnit gas to escape through said pores when the melting point ofsaidfilling material is exceeded.

'3. Thedevice as set forth in claim 2 in which said skeleton bodyconsists essentially of alloy steel.

'4. The device as set forth in claim 2 in which said skeleton bodyconsists essentially of tungsten carbide.

5. The device as set forth in claim 2 in which said skeleton bodyconsists essentially ofbronze.

6. The device as set'forth in claim 2 in which said skeletonbody is made.up of cemented particles which are substantially spherical in shape.

7. The device as set forth in claim 2 in' which the material ofsaidporesconsists essentially of Woods metal.

References Cited in the file of this patent UNITED STATES PATENTS1,068,675 Lightfoot July 29, 1913 1,598,382 McNutt Aug. 31, 19262,096,252 Koehring Oct. 19, 1937 2,190,237 Koehring Feb. 13, 19402,198,254 Koehring Apr. 23, 1940 2,273,589 Olt Feb. 17, 1942 2,518,253Reis Aug. 8, 1950 2,518,746 Blohmet al Aug. 15, 1950 2,580,426 :I-IeigisJan. 1, 1952

1. IN A SAFETY RELIEF DEVICE FOR GASES UNDER PRESSURE, THE COMBINATIONOF A TANK HAVING A DISCHARGE DUCT AND A SAFETY BURSTING DISK PROVIDING ASEALING CLOSURE FOR SAID DUCT, SAID BURSTING DISK COMPRISING A POROUSSKELETON BODY OF CEMENTED METAL PARTICLES TO PROVIDE A STRONG CREEPRESISTANT BODY, THE PORES OF SAID SKELETON BODY BEING FILLED WITH AREADILY FUSIBLE MATERIAL WHICH MELTS AT TEMPERATURES ABOVE NORMAL TOPERMIT GAS TO ESCAPE THROUGH SAID PORES.